The commercially available parasitic nematode Phasmarhabditis hermaphrodita is an effective biocontrol agent for slugs and particularly Deroceras reticulatum, a widespread pest species. Use of the ...nematode is currently limited by cost and it may be that by developing a fuller understanding of the ecology and behaviour of this nematode, more cost effective application strategies can be developed. We investigated the ability of two strains of P. hermaphrodita (one newly isolated and one that had been maintained in vitro for >15 years) to move through mineral soils and organic media. Active dispersal of both strains was found to be greatest in organic media (bark chips and leaf litter, and to a lesser extent peat) and the nematode was capable of growth and reproduction in leaf litter. Conversely, active dispersal was poor in mineral soils. Nematodes moved further in a clay loam compared with a sandy loam, and moved more at a bulk density of 1.0 vs. 1.2 Mg m-3. However, P. hermaphrodita was capable of moving greater distances in mineral soils by using the earthworm Lumbricus terrestris as a phoretic host. Our data suggest that P. hermaphrodita is a facultative parasite that is adapted to living in leaf litter and organic material where slugs frequently rest. The implications of these findings for using the nematode as a biological control agent for slugs are discussed.
Phasmarhabditis hermaphrodita is a nematode parasite that infects and kills several species of slugs. The nematode is produced commercially as a biological control agent for slug pests of agriculture ...and horticulture. Given the difficulties of distinguishing this species from other nematode species in soil samples, very little is known about its natural ecology or its behaviour and persistence following application for biological control. Here we describe a method to quantify
P. hermaphrodita in soil samples based on real time PCR. We designed primers and a dual labelled fluorescent probe that can be used to quantify numbers of
P. hermaphrodita and which is capable of distinguishing this species from the morphologically identical
Phasmarhabditis neopapillosa. We compared different methods whereby the entire nematode community is extracted prior to DNA extraction, and three methods to extract DNA directly from soil samples. Both nematode extraction and DNA extraction from large (10
g) samples of soil gave reliable estimates of nematode numbers, but methods which extracted DNA from small (1
g or less) soil samples substantially underestimated numbers. However, direct extraction of DNA from soils may overestimate numbers of live nematodes as DNA from dead nematodes was found to persist in soil for at least 6 days. The technique could be modified for detection and quantification of all soil borne parasitic nematodes.
Phasmarhabditis hermaphrodita is a parasitic nematode capable of killing several species of slugs including
Deroceras reticulatum, the most widespread slug pest in the world. This nematode can ...control slug infestations in a wide range of crops such as wheat, lettuce and strawberries. Optimization of this biocontrol agent depends on a proper understanding of the interaction between the host and parasite. In this paper, we investigate the response of
P. hermaphrodita to the presence of slug mucus on plates of agar. We define an attraction index and find that the nematodes are significantly attracted by filter paper impregnated with slug mucus compared to paper impregnated with water. Second, nematode trails were recorded on a homogeneous layer of technical agar, with or without the presence of the slug mucus. Mucus was applied in two treatments comprising localization on a piece of filter paper and a uniform distribution across the plate. The different mucus treatments induced significantly different effects on the speed of nematode movement and the distribution of the turning angles, as well as the fractal dimension of nematode foraging trail. These results are consistent with the hypothesis that the nematodes exhibit both a chemotactic and chemokinetic response to a signal emanating from slug mucus.
Abstract
The soil-dwelling nematodes Steinernema carpocapsae, S. scapterisci, S.
feltiae, S. glaseri, Heterorhabditis bacteriophora, H. megidis,
Phasmarhabditis hermaphrodita and Caenorhabditis ...elegans were placed on agar
plates each containing four substrates (peat, sand, sandy loam and leaf
litter). The body-waving behaviour of infective juveniles was recorded over
a 10-day period in the presence or absence of an insect, Galleria
mellonella, a susceptible host of some species. Body-waving behaviour
differed amongst species and varied significantly in relation to substrate,
time and the presence of G. mellonella. Steinernema carpocapsae showed
body-waving behaviour more than other species and this tendency increased
significantly with time. More S. carpocapsae were seen body waving on peat
and leaf litter than on either sandy loam or sand. Conversely, sand promoted
body waving in S. scapterisci. Body waving by C. elegans was more common on
peat than on any of the other substrates. Heterorhabditis megidis, not
previously known to body wave, did so in low numbers on peat and sandy loam.
The remaining four species did not body wave. Previous work has shown that
the presence of S. glaseri increases body waving by S. carpocapsae. We
investigated whether substrate influenced this interaction and also included
S. scapterisci in the study. The presence of S. glaseri significantly
altered rates of body waving in S. carpocapsae and S. scapterisci in a way
that was substrate-dependent. Our data suggest that body-waving behaviour is
determined by substrate quality and differing body-waving behaviours may be
a mechanism by which nematodes avoid competition.
We exposed three slug species (
Deroceras reticulatum (Müller),
Milax gagates (Draparnaud) and
Limax pseudoflavus L.) to the parasitic nematode
Phasmarhabditis hermaphrodita Schneider.
P. ...hermaphrodita was able to cause mortality and feeding inhibition to both
D. reticulatum and
M. gagates but did not negatively affect
L. pseudoflavus. On dissection of surviving
L. pseudoflavus large numbers of
P. hermaphrodita were found encapsulated in the shell of the slug. We found that by increasing shell size, the slug was able to trap invading nematodes, which could be an immune response to
P. hermaphrodita invasion. This is the first report of a slug defense mechanism to inhibit
P. hermaphrodita.
Over two years, six consecutive field experiments were done in which the chemical molluscicide metaldehyde and the nematode biocontrol agent Phasmarhabditis hermaphrodita (Schneider) were applied at ...the standard field rates to replicated mini-plots successively planted with lettuce, Brussels sprouts, leaf beet and cabbage, to compare the effectiveness of different treatments in reducing slug damage to the crops. Soil samples from each plot were taken prior to the start of the experiments, and then monthly, to assess the populations of slugs, snails, earthworms, nematodes, acarids and collembolans. The experiments were done on the same site and each plot received the same treatment in the six experiments. The six treatments were: (1) untreated controls, (2) metaldehyde pellets, (3 and 4) nematodes applied to the planted area 3 days prior to planting without or with previous application of cow manure slurry, (5) nematodes applied to the area surrounding the planted area 3 days prior to planting, and (6) nematodes applied to the planted area once (only in the first of the six consecutive experiments). Only the metaldehyde treatment and the nematodes applied to the planted area at the beginning of each experiment without previous application of manure significantly reduced slug damage to the plants, and only metaldehyde reduced the number of slugs contaminating the harvested plants. The numbers of slugs, snails and earthworms in soil samples were compared among the six treatments tested: with respect to the untreated controls, the numbers of Deroceras reticulatum (Muller) were significantly affected only in the metaldehyde plots, and the numbers of Arion ater L only in the plots treated with nematodes applied to the planted area 3 days prior to planting without previous application of manure; numbers of snails (Ponentina ponentina (Morelet) and Oxychilus helveticus (Blum)) were not affected by the treatment. The total numbers of all earthworm species and of Lumbricus spp were unaffected by the treatment, but Dendrobaena spp increased significantly in the plots treated with manure. The numbers of nematodes, acarids and collembolans in soil samples were compared between the untreated controls and the treatments with nematodes applied 3 days prior to planting to the planted area or to the surrounding area, without previous application of manure: the treatment had a significant effect on the number of nematodes in soil samples, but acarids and collembolans were unaffected.
Slugs are a serious pest in floriculture, horticulture, and agriculture in many parts of the world, and Deroceras reticulatum is generally the most destructive species. A molluscicidal nematode, ...Phasmarhabditis hermaphrodita, has potential for the biological control of pest slugs, but application rates of 3.0 × 109 infective juveniles (IJs)/ha are usually required for effective plant protection, rendering applications very expensive. The nematodes are usually applied as an overall application to the surface of soil to provide uniform coverage of the entire area. However, slugs possess a well-developed homing behavior with an ability to locate homing sites or shelters from over a meter away. As slugs are nocturnal foragers and spend significant time in the homing sites during the day, we hypothesized that the application of nematodes to the homing sites may be as effective as the overall application to the entire area. This hypothesis was tested in a newly designed bioassay arena consisting of 90 × 68 × 36-cm-deep plastic tubs mounted with copper slug barriers. Each tub contained muck soil to a depth of 15 cm, four Impatiens or Hosta plants, and 12 adult D. reticulatum slugs. The nematode, P. hermaphrodita, was applied at 0.3 × 106 or 0.6 × 106 IJs/m2 either to the entire area or only under a 30 by 30-cm roofing shingle that served as an artificial slug shelter. A standard chemical molluscicide, metaldehyde, and an untreated control treatment were included for comparison. Although metaldehyde caused more rapid slug mortality than the nematodes, the nematodes provided plant protection (i.e., number of leaves damaged and leaf area eaten) equal or better than metaldehyde. Overall, the nematode application rate of 0.6 × 106 IJs/m2 applied only under the shingles provided equally or more effective plant protection than the application of nematodes to the entire area at 0.3 × 106 IJs/m2. This represents a 63% reduction in the total number of nematodes required to treat the same area (i.e., 1.1 × 109 IJs/ha vs 3.0 × 109 IJs/ha). The additional presence of recycled nematodes provided 96–100% control of the reintroduced slugs. Even the low rate (0.3 × 106 IJs/m2) applied only under shingles was as effective as the high rate (0.6 × 106 IJs/m2) applied as an overall treatment to the entire area. We conclude that the application of P. hermaphrodita to slug shelters may provide more economical control than the overall application to the entire area.
Summary
In a replicated field experiment, ryegrass, vetch and red clover were grown or the soil was kept bare over a 2–month period in summer to compare the effects of these treatments on slug damage ...to the following crop (Chinese cabbage) and on the efficacy of nematodes (Phasmarhabditis hermaphrodita) applied as biological control agents to the soil at planting time to protect this crop. Slug damage was significantly (c. two times) greater after red clover or vetch than after ryegrass. Damage on plots without cover crop was intermediate and not significantly different from either extreme. Slug damage was reduced by about one‐third by the nematode treatment. The preceding cover crop did not influence nematode efficacy. Numbers of slugs on harvested plants (mainly Deroceras reticulatum and Deroceras panormitanum) were influenced by an interaction between cover crop and nematode treatment. On subplots without nematodes, more slugs were recorded with than without a preceding cover crop. No such differences were found on nematode‐treated subplots. Soil samples were collected at intervals from 0–99 days after nematode treatment to monitor nematode survival and infectivity in bioassays with D. reticulatum. No significant effects of cover crops were detected in bioassays. Moreover, there were no significant effects of nematodes on slug survival. Their effects on slug food consumption were mostly insignificant and any effects were transient and not consistent. However, significantly more slug cadavers contained nematodes when slugs were exposed to nematode‐treated soil. The implications of these results are discussed.
The nematode Phasmarhabditis hermaphrodita is a commercially available biocontrol agent against slugs. This product is especially interesting for use in organic farming, where products containing ...metaldehyde or carbamates cannot be used for controlling pest slugs. We investigated the potential of P. hermaphrodita for the control of the pest slugs Deroceras reticulatum and Arion lusitanicus. These two species are the most harmful slug pests in Switzerland. At different times of the year, we collected slug specimens of different weight and assessed their susceptibility to P. hermaphrodita in the laboratory. Batches of five slugs were subjected to five different doses of nematodes plus an untreated control and replicated three times. During six weeks, feeding and survival of the slugs were recorded. D. reticulatum was strongly affected by increasing nematode doses, irrespective of the slugs' body weight. In small specimens of A. lusitanicus, feeding and survival were strongly affected by the nematodes, while larger specimens remained almost unaffected. Because A. lusitanicus has an asynchronous development in Switzerland, it seems difficult to control the entire population with a single nematode application. To what extent nematodes will be used in practice for slug control depends on their effectivity against the pest slugs of major importance, on the longevity of the molluscicidal effect and on the price of nematodes.
